Burned periclase brick and method of making

ABSTRACT

Burned periclase brick is prepared from a size-graded batch of calcined magnesite in which the relatively coarse fraction (+48 mesh) has a CaO:SiO2 weight ratio of from above 2:1 to about 5:1 but the relatively fine fraction (-48 mesh) has a CaO:SiO2 weight ratio of from about 1.5:1 to below 2:1.

United States Patent Treffner et a1.

[ 51 Oct. 29, 1974 BURNED PERICLASE BRICK AND METHOD OF MAKING Inventors: Walter S. Treffner, Linthicum Heights; Frank P. Filer, Baltimore, both of Md.

Assignee: General Refractories Company,

Philadelphia, Pa.

Filed: June 12, 1972 Appl. No.: 261,987

Related US. Application Data Continuation of Ser. No. 16,237, March 3, 1970,

abandoned.

US. Cl. 106/58 Int. Cl C04b 35/04 Field of Search 106/58 [56] References Cited UNITED STATES PATENTS 3,141,790 7/1964 Davies et a1. 106/58 3,248,240 4/1966 Heuer 106/58 Primary ExaminerJ. Poer Attorney, Agent, or Firm1-lowson and l-lowson [5 7 ABSTRACT 10 Claims, No Drawings BURNED PERICLASE BRICK AND METHOD OF MAKING BACKGROUND OF THE INVENTION This is a continuation, of application Ser. No. 16,237 filed Mar. 3, 1970, now abandoned.

Burned periclase bricks are well known and are especially useful as linings in a basic oxygen furnace. Such bricks are prepared by pressing a size-graded mixture of calcined magnesite particles, containing a small amount of an aqueous solution of a preliminary binder like magnesium sulfate, magnesium chloride or a lignosulfonate, into brick form and firing at a temperature of from about 2,900 to about 3,100F. The use of highpurity magnesite or periclase (e.g., 95% MgO and higher) having a CaOzSiO ratio of over 2:1 has been proven advantageous. Such magnesites contain dicalcium silicate as principal impurity which is known to provide an excellent, very refractory bonding phase resulting in very good hot strengths in burned brick using such magnesite. It is also known that even small boron contents can effectively destroy the high-temperature strength of such compositions (e.g., US. Pat. No. 3,275,461). Normally the entire batch mix of sizegraded calcined magnesite, fines as well as coarses, has the same chemical composition including limezsilica ratio. Some consideration has been given, in the manufacture of burned periclase bricks, to the limezsilica ratio of the material. For example, US. Pat. No. 3,275,461 refers to a CaO1SiO ratio of at least 2:1 (in conjunction with other features, such as B content) as providing better results than CaOzSiO ratios below 2: 1, such as 1.4:1 to 1.7:]. Consideration has also been given to the CaOzSiO ratio in other types of refractories. For example, US. Pat. No. 3,141,917 is directed to a tar bonded basic brick in which the fines have a CaOzSiO ratio of over 2:].

It has been found, however, that in the manufacture of burned periclase brick control of the CaOzSiO ratio of the fines at from about 1.5:1 to below 2:1 with the CaOzSiO ratio of the coarses being from above 2:1 to about :1, there is a marked improvement in hot physical properties of the resulting brick, principally in its hot transverse strength and its hot compressive strength.

Therefore, the method of the present invention comprises, in the manufacture of a burned periclase brick wherein a mixture of relatively coarse calcined magnesite having a particle size such that substantially all thereof passes a 3-mesh screen and is retained on a 48- mesh screen and of relatively fine calcined magnesite having a particle size such that substantially all thereof passes through a 48-mesh screen and the relatively coarse calcined magnesite makes up from about 50 to about 80 percent by weight, of said mixture, is pressed into brick form and fired at a temperature of at least about 2,900F., the improvement wherein said relatively coarse calcined magnesite has a CaOzSiO weight ratio of from above 2:1 to about 5:1 but the relatively fine calcined magnesite has a CaOzSiO weight ratio of from about 1.521 to below 2:1.

The resulting brick thus comprises a burned periclase brick in which the defined mixture of calcined magnesite particles are ceramically bonded together.

It has been found that unexpected additional benefits of dicalcium silicate bonding can be obtained when at least a portion of the dicalcium silicate is formed in situ during burning the brick. This is preferably done at the boundaries between the relatively coarse and the relatively fine particles in the brick by changing the chemistry, and consequently the composition, of the accessory mineral phases of the relatively fine particles of the brick thus creating a chemical composition gradient between the relatively coarse and the relatively fine fractions of the brick. The constituents of the more siliceous fine particles will react with the constituents of the less siliceous coarse particles forming, during the firing of the brick, refractory dicalcium silicates thus forming a bond of a high hot strength between the relatively coarse and the relatively fine particles of the brick. The reaction also forms some secondary periclase and it is believed also to promote direct periclaseto-periclase bonding thus further contributing to increased high-temperature strength.

Calcined magnesite is the basic component of the bricks prepared according to the present invention. The calcined magnesite will generally have an MgO content of at least percent and preferably at least percent, the balance being small and varying amounts of lime (CaO) and silica (SiO and miscellaneous oxides of aluminum, iron, manganese, etc. As is customary practice, the batch mix of calcined magnesite will be size graded to provide a relatively coarse fraction (coarses) and a relatively fine fraction (fines). The relatively coarse fraction has a particle size distribution such that substantially all thereof passes through a 3-mesh screen and is retained on a 48-mesh screen, whereas the relatively fine fraction has a particle size such that substantially all thereof passes through a 4'8- screen. Mesh sizes herein refer to Tyler mesh series. The coarse fraction will make up from about 50 to 80 percent, preferably from about 60 to about 70 percent, by weight, of the mixture of coarses and fines.

According to the present invention the relatively fine fraction will have a CaO:SiO weight ratio lower than that of the relatively coarse fraction. Thus, the relatively coarse fraction will have a CaOzSiO ratio of from above 2:1 to about 5:1. The relatively fine fraction, on the other hand, will have a CaOzSiO ratio of from about 1.5:1 to below 2:1, with a CaO:SiO ratio of about 1.6 1.85:1 being particularly preferred. The relatively fine fraction having the stated CaO2SiO ratio is preferably the natural ball mill fines of a calcined magnesite having the desired low CaOzSiO ratio so that no adjustment is necessary. However, if the principal fines material available has a CaO:SiO ratio above the desired level, its CaO:SiO ratio can be adjusted to the desired lower level by mixing with it a fine silicabearing material having a very low CaOzSi0 ratio such as a silica-rich calcined magnesite, talc, serpentine, olivine, silica fines, or the like. On the other hand, relatively fine calcined magnesite having a CaO:SiO below the desired level can have its ratio adjusted upwardly by mixing with it a fine lime-bearing material having a high CaO:SiO ratio such as a lime-rich calcined magnesite, calcium carbonate, dolomite or the like.

The nature and amount of CaOzSiO ratio adjustment in the fines, if resorted to, may be governed by the particular improvement desired. Thus, optimum improvement in hot transverse strength is achieved at a CaO:- SiO ratio of about 1.6:1 when the calcined magnesite used in preparing (ball milling) the fines has that natural ratio. Satisfactory hot transverse strengths can also be achieved by adjusting downwardly a CaO1SiO ratio higher than desired unless the latter is well over 2:1. However, even in this latter case, firing the brick at higher than usual temperatures, discussed more in detail hereinafter, can afford an improvement in hot transverse strength. High hot compressive strengths are obtained with fines having CaOzSiO ratios of 1.6 1.9:1 whether they be natural (virgin) fines or fines of an initially higher CaOzSiO- which have had their CaOzSiO ratio adjusted downwardly. The use of firing temperatures higher than usual further improves the hot compressive strength.

Once the batch mix of size graded calcined magnesite having the defined CaOzSiO ratios in the coarse and fine fractions has been prepared, standard burned brick-making practice may be followed. Thus, a small amount of an aqueous temporary or preliminary binder may be mixed with the calcined magnesite, and the damp mixture is pressed into brick form. The bricks may then be fired following conventional practice at a temperature of from about 2,900 to about 3,100F., as in a tunnel kiln. However, as mentioned above, further improvement in hot strengths can be realized by firing at temperatures higher than usual, namely to temperatures of from about 3,100 to about 3,300F.

The present invention will be more readily understood from a consideration of the following specific examples which are given for the purpose of illustration only and are not intended as limiting the scope of the invention in any way.

EXAMPLE 1 1n this Example bricks are prepared from a batch mix of 65 parts, by weight, of coarse calcined magnesite +14 do. 80.3 +20 do. 39.9 +2.8 do. 95.6 28 do. 44

and an oxide analysis as follows:

MgO 96.30% (a0 2.4m sio, 0.99%

oxides of Fe. Al. Mn, etc. 41.25%

The fine fraction had a particle size distribution as follows:

+48 mesh 2.471 +65 do. 8.5 +100 do. 20.7 +200 do. 38.8 +325 do. 467 325 do. 5 3.3

The fine fraction differed, as set forth in Table l, in terms of CaO:SiO ratio. Where the CaOzSiO was adjusted upwardly, fine calcium carbonate powder was added until the desired CaOzSiO ratio was provided; and where the CaOzSiO ratio was adjusted downwardly a fine calcined magnesite having a low CaO:- SiO- ratio was added until the desired ratio was reached.

The bricks were prepared by mixing the grain mix with l percent of a percent aqueous solution of lignosulfonate and 1.1% H 80 (as dilute sulfuric acid) and pressing the damp mixture at 12,000 psi. The bricks were then fired at 3.000F. in a tunnel kiln following which physical properties were measured as set forth in Table 1. The results are tabulated as follows:

Pcriclase Brick Variation in Lime to Silica Ratio of Fines 3000F Tunnel Kiln Burn me to mm mm of Fines: 1.61 1 83 Ratio of Fines Adjusted From: 2.65 2.15 1.83 2.65 2.15 1.61

Bulk Density, oz/inf 1.71 1.71 1.72 1.70 1.70 1.71 1.72 1.70

lcc 2.96 2.96 2.98 2.94 2.94 2.96 2.98 2.94 i!!! of UQIH p.s.i. 1 4, 7. 2. .2 .99. 19 11 I355. 96. 2030 Cold Crushing Strength, p.s.i. 61 10 4720 5070 6775 4280 4250 5155 5160 Modulus of Rupture at 2700F, p.s.i. 1285 1325 1610 1660 1290 1200 1195 1125 Compressive Strength at 2800F, p.s.i. 2785 2095 3305 2620 2830 2435 2865 2425 Porosity. Open. 15.2 15.4 14.8 16.7 15.7 15.0 14.7 16.4 Lime to Silica Ratio of Fines: 2.15 2 Ratio of Fines K8 usted From: 2.65 1.83 1.61 2 15 1.83 l 61 Bulk Eenstty, oz.7in.' 1.70 1.70 1.71 1.70 1.70 1.71 1.70 1.69 glcc 2.94 2.94 2.96 2.94 2.94 2.96 2.94 2.92 Modulus of Rupture, p.s.i. 1770 1340 1770 1835 1805 1810 1780 1715 Cold Crushing Strength, p.s.i. 3980 3720 3980 5155 3805 4365 3700 5075 Modulus of Rupture at 2700F, p.s.i. 1245 995 1025 1000 1130 825 1240 1045 Compressive Strength at 2800F, p.s.i. 2230 1780 2705 1920 2305 1935 1935 I790 Porosity. Open, 15.6 15.5 15.6 16.7 15.9 15.3 14.9 16.3

Natural ball mill fines (no adjustment) EXAMPLE 2 and 35 parts, by weight. of fine calcined magnesite The coarse fraction had a particle size distribution as follows:

+4 mesh 0.3% +0 do. 14.6 +8 do. 39.5 +11) do. 65.8

In this Example, the procedure of Example 1 was followed except that the bricks were fired at 3,170F. in a laboratory kiln.

The results are tabulated as follows:

Table 2 Periclase Brick Variations in Lime to Silica Ratio of Fines 3170F Laboratory Burn Lime to Silica Ratio of Fines: 1.61 1.83 Ratio oi Fines Adjusted From: 2.65 2.15 1.83 2.65 2.15 1.61

Bulk Density, ozJin. 1.72 1.72 1.72 1.71 1.71 1.72 1.71 1.71 g/cc 2.98 2.98 2.98 2.96 2.96 2.98 2.96 2.96 Modulus of Rupture, p.s.i. 2485 2550 2450 2790 2740 2570 2370 2660 Cold Crushing Strength, p.s.i. 5545 4715 4550 6510 5420 4970 4660 5770 Modulus of Rupture at 2700F, p.s.i. 1740 1450 1845 2040 1725 1450 1835 1765 Compressive Strength at 2800F. p.s.i. 4275 4240 2970 3535 4975 4270 4080 3415 Porosity. Open, Ir 15.4 15.0 15.1 16.3 15.1 14.8 15.4 16.3 Lime to Silica Ratio of Fines: 2.15 2.65

am) Ines usted mm: 2.65 1.83 1.61 2.15 1.83 1.61 Bulk Density. o7../in. 1.71 1.71 1.71 1.70 1.70 1.72 1.71 1.69 g/cc 2.96 2.96 2.96 2.94 2.94 2.98 2.96 2.92 Modulus of Rupture, p.s.i. 2805 1875 2370 2245 2240 2110 2220 2260 Cold Crushing Strength. p.s.i. 5350 4010 4660 4810 4385 3495 3370 4850 Modulus of Rupture at 2700C. p.s.i. 1560 1535 1530 1350 1220 1245 1230 1225 Compressive Strength at 2800C. p.s.i. 3670 3695 4080 3030 2785 3075 3150 2475 Porosity. Open. 74 15.4 15.6 15.4 16.3 16.4 15.0 15.4 16.6

Natural ball mill fines (no adjustment) What is claimed is? W 1. 1n the manufacture of a burned periclase brick having a MgO content of at least 90 percent by weight wherein a mixture of relatively coarse calcined magnesite having a particle size such that substantially all thereof passes through a 3-mesh screen and is retained on a 48-mesh screen and of relatively fine fraction having a particle size such that substantially all thereof passes through a 48-mesh screen and the relatively coarse calcined magnesite makes up from about 50 to about 80 percent, by weight, of said mixture, is pressed into brick form and fired at a temperature of at least 2,900F., the improvement wherein said relatively coarse calcined magnesite has a CaO:SiO Weight ratio of from above 2:1 to about 5:1 and the relatively fine fraction has a CaO:SiO weight ratio of from about 1.5:1 to below 2:1.

2. The method of claim 1 wherein said relatively fine calcined magnesite has a CaOzSiO weight ratio of from about 1.6:1 to about 1.85:1.

3. The method of claim 1 wherein said relatively fine calcined magnesite has a CaOzSiO- weight ratio of about 1.621.

4. The method of claim 1 wherein said relatively fine calcined magnesite consists essentially of natural ball mill fines of a calcined magnesite.

5. The method of claim 2 wherein said relatively fine calcined magnesite consists essentially of natural ball mill fines of a calcined magnesite.

6. The method of claim 1 wherein said brick is fired at a temperature of from about 3.100 to about 3,300F.

7. The method of claim 2 wherein said brick is fired at a temperature of from about 3,100 to about 3,300F.

8. in a burned periclase brick having a MgO content of at least 90 percent by weight wherein calcined magnesite particles are ceramically bonded together, the calcined magnesite being a mixture of a relatively coarse fraction having a particle size such that substantially all thereof passes through a 3-mesh screen and is retained on a 48-mesh screen and of a relatively fine fraction having a particle size such that substantially all thereof passes through a 48-mesh screen and the relatively coarse fraction makes up from about 50 to about percent, by weight, of the mixture, the improvement wherein said relatively coarse fraction has a CaOzSiO weight ratio of from above 2: 1 to about 5:1 but the relatively fine fraction has a CaOzSiO weight ratio of from about 1.511 to below 2:1.

9. The brick of claim 8 wherein said relatively fine fraction has a CaOzSiO weight ratio of from about 1.611 to about 1.85:1.

10. The brick of claim 9 wherein said relatively fine fraction has a CaO2SiO weight ratio of about 1.6: 1. 

1. IN THE MANUFACTURE OF A BURNED PERICLASE BRICK HAVING A MGO CONTENT OF AT LEAST 90 PERCENT BY WEIGHT WHEREIN A MIXTURE OF RELATIVELY COARSE CALCINED MAGNESITE HAVING A PARTICLE SIZE SUCH THAT SUBSTANTIALLY ALL THEREOF PASSES THROUGH A 3-MESH SCREEN AND IS RETAINED ON A 48-MESH SCREEN AND OF RELATIVELY FINE FRACTION HAVING A PARTICLE SIZE SUCH THAT SUBSTANTIALLY ALL THEREOF PASSES THROUGH A 48-MESH SCREEN AND THE RELATIVELY COARSE CALCINED MAGNESITE MAKES UP FROM ABOUT 50 TO ABOUT 80 PERCENT, BY WEIGHT, OF SAID MIXTURE, IS PRESSED INTO BRICK FORM AND FIRED AT A TEMPERATURE OF AT LEAST 2,900*F. THE IMPROVEMENT WHEREIN SAID RELATIVELY COARSE CALCINED MAGNESITE HAS A CAO:SIO2: WEIGHT RATIO OF FROM ABOUT 2:1 TO ABOUT 5:1 AND THE RELATIVELY FINE FRACTION HAS A CAO:SIO2 WEIGHT RATIO OF FROM ABOUT 1.5:1 TO BELOW 2:1.
 2. The method of claim 1 wherein said relatively fine calcined magnesite has a CaO:SiO2 weight ratio of from about 1.6:1 to about 1.85:1.
 3. The method of claim 1 wherein said relatively fine calcined magnesite has a CaO:SiO2 weight ratio of about 1.6:1.
 4. The method of claim 1 wherein said relatively fine calcined magnesite consists essentially of natural ball mill fines of a calcined magnesite.
 5. The method of claim 2 wherein said relatively fine calcined magnesite consists essentially of natural ball mill fines of a calcined magnesite.
 6. The method of claim 1 wherein said brick is fired at a temperature of from about 3,100* to about 3,300*F.
 7. The method of claim 2 wherein said brick is fired at a temperature of from about 3,100* to about 3,300*F.
 8. In a burned periclase brick having a MgO content of at least 90 percent by weight wherein calcined magnesite particles are ceramically bonded together, the calcined magnesite being a mixture of a relatively coarse fraction having a particle size such that substantially all thereof passes through a 3-mesh screen and is retained on a 48-mesh screen and of a relatively fine fraction having a particle size such that substantially all thereof passes through a 48-mesh screen and the relatively coarse fraction makes up from about 50 to about 80 percent, by weight, of the mixture, the improvement wherein said relatively coarse fraction has a CaO:SiO2 weight ratio of from above 2:1 to about 5:1 but the relatively fine fraction has a CaO:SiO2 weight ratio of from about 1.5:1 to below 2:1.
 9. The brick of claim 8 wherein said relatively fine fraction has a CaO:SiO2 weight ratio of from about 1.6:1 to about 1.85:1.
 10. The brick of claim 9 wherein said relatively fine fraction has a CaO:SiO2 weight ratio of about 1.6:1. 